Current evidence on potential of adipose derived stem cells to enhance bone regeneration and future projection

Table 3 Specific markers used for selection of sub-populations of adipose derived stem cells showing superior bone forming ability

Ref.	Marker	Study outcome and salient findings
	CD146
James et al[110]	CD146+CD34-CD45- (Pericytes) + CD146-CD34+CD45- (Adventitial cells)	Intramuscular ectopic bone formation in SCID mice; FACS purified, human, pericytes + adventitial cells produced significantly more ectopic bone formation than SVF; BMP2 enhanced osteogenic as well as adipogenic differentiation, whereas Nel-1 promoted only bone formation when tested in ectopic bone formation assay; 250000 cells were implanted intramuscularly in SCID mice for 4 wk using collagen sponge or DBX+ β-TCP + 3.5 -11.25 µg of BMP2 or 350 µg Nel-1
James et al[109]	CD146+CD34-CD45- (Pericytes) + CD146-CD34+CD45- (Adventitial cells)	Human pericytes + adventitial cells together make up around 40% of SVF from human lipoaspirate (60 patients tested) both types representing around 20% and these numbers do not change with age, gender, or body mass index; FACS purified, human, pericytes + adventitial cells induce significantly more healing in mouse calvarial defect than SVF; 250000 cells were implanted to critical size (3 mm) calvarial defect in SCID mice for 8 wk using PLGA
Meyers et al[112]	CD146+CD34-CD45- (Pericytes) + CD146-CD34+CD45- (Adventitial cells)	It was feasible to purify human pericytes + adventitial cells using a multi-column approach of magnetic beads; Purified pericytes + adventitial cells could enhance critical size (4 mm) calvarial defect created in SCID mice; 250000 cells were implanted to critical size (4 mm) calvarial defect in SCID mice for 8 wk using PLGA
	CD90
Chung et al[115]	CD90+	CD90+ cells induced almost complete healing of critical size (4 mm) calvarial defect in nude mice compared to CD105low (approximately 75%), CD105high - (approximately 65%), and CD90- (40%) by micro-CT; Taken together CD90+ cells are more osteogenic compared to CD105low cells; 150000 cells were implanted to critical size (4 mm) calvarial defect in SCID mice for 8 wk using PLGA
Ferraro et al[113]	CD90+CD34+	Implantation of human CD90+CD34+ ADSCs in nude mice resulted in the formation of only fat tissue surrounded by loose connective tissue; 250000 cells were implanted subcutaneously in nude mice for 4 wk using a collagen sponge
	CD105
Levi et al[120]	CD105low	FACS-sorted, human, CD105low sub-population of ADSCs significantly enhanced bone regeneration (> 95%) in critical size (4 mm) calvarial defect in CD1-nude mice compared to CD105high (approximately 40%) and unsorted ADSCs (50%-60%); Knockdown of CD105 in ADSCs (shCD105) resulted in improving their ability to induce bone formation (> 60%) compared to ADSCs transfected with control shRNA (30%); 150000 cells were implanted to critical size (4 mm) calvarial defect in nude mice for 8 wk using PLGA-HA
Madhu et al[123]	CD105+CD34-; CD105+ CD34+; CD105-CD34+; CD105-CD34-	FACS-purified, mouse, CD105+CD34− ADSCs that responded maximally to BMPs in vitro failed to induce ectopic bone formation upon their sub‐cutaneous implantation immunocompetent syngeneic mice; FACS-purified CD105-CD34- ADSCs responded the least to BMPs in vitro. A bone marrow-derived, clonal, osteoprogenitor population showing the similar phenotype of CD105-CD34- induced robust bone formation; OM preconditioned 1 × 106 cells were implanted subcutaneously in Balb/c mice for 4 wk using Matrigel
Chan et al[128]	AlphaV+CD200+CD105-D90-	Mouse skeletal stem cells that give rise to bone were identified as AlphaV+CD200+CD105-D90- cells and were present in the femoral growth plate; They were not present in adipose tissue; however, when a collagen sponge loaded with BMP-2 was implanted in adipose tissue, the authors reported de novo formation of AlphaV+CD200+CD105-D90- cells in the adipose tissue; Subcutaneous implantation of 10 µg BMP2+ Collagen Sponge in nude mice for 4 wk
Chan et al[131]	PDPN+CD164+CD73+ CD146-	The human counterpart of mSSC was discovered and was found to be of phenotype PDPN+ CD164+CD73+ CD146-; Human adipose stroma did not naturally contain these cells but when it was mixed with BMP-2 and injected sub-cutaneously it led to skeletal reprogramming and induced formation of PDPN+ CD164+CD73+ CD146- human skeletal stem cells; 10 × 106 cells with 10 µg BMP2 + Matrigel were subcutaneously implanted in nude mice for 4 wk
	CXCR4
Xu et al[133]	CXCR4+	CD146+CD34-CD45- cells were FACS-purified from hard (human periosteum) and soft (adipose and dermal tissue). Cells isolated from hard tissue but not the soft tissues showed a strikingly high tendency for skeletogenesis; This corresponded to high CXCR4 signaling in periosteal cells; Inhibition of CXCR4 signaling abrogated bone-forming potential of CD146+CD34-CD45- periosteal cells; CXCR4+ cells from soft tissue (adipose) derived CD146+CD34-CD45- cells represented osteoblastic/non-adipocytic precursor cells; 1 × 106 cells were implanted intramuscularly in nude mice for 4 wk using DBM putty
	PDGFRα
Wang et al[134]	PDGFRα+	Lineage tracing using PDGFRα reporter mice showed that PDGFRα expression marks different sub-populations in the adipose tissue; PDGFRα+ and PDGFRα− fractions both are multipotent progenitor cells, however, PDGFRα+ ADSCs-derived ectopic implants ossify to a greater degree than PDGFRα− cell fractions; 1 × 106 PDGFRα+ or PDGFRα- cells were implanted intramuscularly in nude mice for 8 wk using HA-β-TCP; Or Subcutaneous implantation of 2.5 µg BMP2 + Matrigel into the inguinal fat pad of PDGFRα+ -CreER for 8 wk

ADSC: Adipose-derived stem cells; FACS: Fluorescence-activated cell sorting; SCID: Severe combined immunodeficiency; BMP: Bone morphogenetic protein; TCP: Tricalcium phosphate; PLGA: Polylactic glycolic acid; HA: Hydroxyapatite; DBM: Demineralized bone matrix.